Production of carrageenan can be traced back to Ireland where plants of the red seaweed algae species chondrus crispus were first harvested with rakes during low tide or by gathering seaweed that had washed ashore. After harvesting, the weeds were typically washed, sun-bleached, dried and boiled with milk to form a pudding. The weeds themselves were dubbed “Irish Moss” and after making it familiar to most of Europe, Nineteenth Century Irish immigrants carried it to the U.S. and Canada as well.
Today, this seaweed pudding is mostly confined to Ireland's cultural history, but carrageenan has become much more important because of its effectiveness as a functional food additive in forming gels in an aqueous system, which make it useful in a wide variety of applications, including beer (in which it has been used for over 150 years as a fining) to processed meat and food products like milk drinks and deserts; pharmaceutical preparations such as orally-administered gelcaps; personal care products such as toothpaste and skin care care preparations; and household products such air-freshener gel and cleaning gels. The temperature at which carrageenan gels and melts is dependent on a number of factors that include especially the concentration of gelling cations such as potassium and calcium ions. Generally speaking, the higher the concentration of gelling cations the higher the gelling and melting temperature of the carrageenan. Such cations may come not only from the composition to which the carrageenan is added as a gelling agent, but also from the carrageenan itself.
Thus, carrageenans with relatively high gelling cation concentrations also require relatively high-temperature processing. Generally, lower temperature processes are preferred since these save processing time, are less expensive and don't negatively affect the preparation of the composition in which the carrageenan is being included—this is especially important for food compositions, where higher temperatures may impair the base foodstuffs that are included in the food product. Thus, in order to produce carrageenan materials that promote gelling at even lower temperatures there is a continuing need for carrageenan extraction methods that reduce the concentration of gelling cations in the carrageenan.
Contemporary methods of carrageenan extraction and production have advanced considerably in the last fifty years. Perhaps most significantly is that today, rather than being gathered from wild-grown seaweed, carrageenan-containing plants such as Kappaphycus cottonii (Kappaphycus alvarezii), Euchema spinosum (Euchema denticulatum), and the above mentioned Chondrus crispus are more commonly seeded along nylon ropes and harvested in massive aqua-culture farming operations particularly in parts of the Mediterranean and throughout much of the Indian Ocean and along the Asian Pacific Ocean Coastline. Just as in the Nineteenth-century process, in contemporary processes before further processing the seaweed raw materials are first thoroughly cleaned in water to remove impurities and then dried. Then, as described in U.S. Pat. No. 3,094,517 to Stanley et al. the carrageenan is extracted from the cleaned seaweed while also at the same time being subjected to alkali modification by placing the seaweed in solution made slightly alkaline by the addition of a low concentration of alkali salt (i.e., a pH of the solution is raised to a range of, e.g., 9-10) and then heating this solution to a temperature of around 80° C. for a period of time of about 20 minutes to as long as two hours.
Subjecting the carrageenan-containing seaweed to alkali modification has the desired result of reducing the gelling cation concentration in the resulting carrageenan product; however, the extent to which the gelling cation levels can be reduced is limited because only relatively low concentrations of alkali may be used so as to not depolymerise (and thus damage) the carrageenan in the seaweed. So even though the gelling cation concentrations are reduced, they still remain high.
For example, when an alkali modification process is NOT used, typical cation concentration levels are:                Potassium: About 4%        Calcium: About 0.6%        Magnesium: About 0.7%        Sodium: About 3%        
When an alkali modification step is used to reduce these gelling cation
concentrations, such as in U.S. Pat. No. 3,094,517 (Stanley et al.), which makes use of calcium hydroxide as alkali modification agent, the resulting cation concentration levels are:                Potassium: About 5%        Calcium: About 3%        Magnesium: About 0.1%        Sodium: About 2%        
As can be seen, the alkali modification step taught in U.S. Pat. No. 3,094,517 significantly reduced the levels of magnesium and sodium ions, but not other gelling cations such as potassium and calcium. Accordingly, other alkalis have been proposed. For example in U.S. Pat. No. 6,063,915 to Hansen et al., sodium hydroxide and sodium bicarbonate were used as alkalis, producing carrageenans with the following cation concentrations:                Potassium: About 5%        Calcium: About 0.05%        Magnesium: About 0.01%        Sodium: About 5%        
While the process taught in U.S. Pat. No. 6,063,915 produces the carrageenan
having the best cation gelling concentration profile currently available, the levels of other gelling cations are still somewhat high, making it impossible to further reduce the gelling and melting temperature of compositions containing the carrageenans.
Given the foregoing there is a need in the art for carrageenans having reduced gelling cations, and thereby lower gelling and melting temperatures, but without having been depolymerised or damaged so as to be non-functional.